Factors influencing the restitution of the duodenal and colonic mucosa after damage

Rapid epithelial restitution is an important protective mechanism which enables the gastrointestinal mucosa to reestablish epithelial integrity following superficial injury within hours. In this study we examined the influence of an acidic luminal pH, removal of the necrotic layer, nutrient bicarbonate, calcium and sodium desoxycholate (Na-DOC) on restitution in the rabbit duodenum in vitro and the role of Na-DOC and calcium for rapid restitution of the human colon in vitro. Transmucosal potential difference (PD), short-circuit current (lsc) were measured and resistance against passive ion flux (R) was calculated. Electrophysiological changes paralleled morphological injury but did not necessarily reflect restitution in all experiments. The extent of mucosal injury was assessed by computerized real-time morphometry. 5 hrs after luminal exposure to 10 mH HCl for 10 min residual damage (RD) was 14% in the duodenum. Luminal pH of 3.0 (RD of 30%), removal of necrotic layer at acidic luminal pH (RD of 66%), absence of bicarbonate from the serosal solution (RD of 35 % at neutral luminal pH; RD of 96% at acidic luminal pH) and removal of calcium from the serosal solution (RD of 58 %) impaired restitution in the duodenum. Continuous postinjury luminal Na-DOC exposure did not influence restitution in the duodenum (RD of 19%). 5 hrs after luminal exposure to 0.5 mM Na-DOC for 10 min RD was 26% in the human colon. Continuous postinjury luminal Na-DOC exposure (RD of 51 %) and removal of calcium from the nutrient solution (RD of 65 %) impaired restitution in the human colon. Thus we conclude that restitution of the rabbit duodenum in vitro requires a necrotic layer and bicarbonate flux to withstand acidic luminal pH, while restitution is not Effected by Na-DOC. In the human colon Na-DOC inhibits restitution. Both the duodenum and colon require calcium for rapid restitution.